Electric machines in the form of polyphase machines operated in conjunction with inverters are usually used to drive hybrid vehicles or electric vehicles. The electric machines are operated optionally in motor mode or in generator mode. In motor mode, the electric machine generates a driving torque which supports an internal combustion engine when used in a hybrid vehicle, for example, during an acceleration phase. In generator mode, the electric machine generates electrical energy, which is stored in an energy storage such as a battery or a Super-Cap, for example. The mode and performance of the electric machine are adjusted via the inverter with the aid of a control unit—often referred to as a machine controller.
Conventionally, continuous torque monitoring is carried out to discover malfunctions in a machine controller of an electric machine. This is used in particular to protect vehicle occupants and external traffic participants. An excessive rise in torque and a resulting inadvertent acceleration or deceleration of the vehicle are to be prevented. The core of continuous torque monitoring is the comparison of an actual torque supplied by the electric machine with an allowed torque. In the normal case, the actual torque is lower than the allowed torque. If the actual torque exceeds the allowed torque, an error is present in the machine controller of the electric machine, and an error response, which results in a safe vehicle condition, is initiated.
In conventional vehicles, the torque of the electric machine is usually calculated on the basis of a mathematical machine model. Consequently, the object of torque monitoring is to check the plausibility of the electromagnetic torque calculated by a machine controller on the basis of a model.
PCT Application No. WO 2007/025839 A1 describes a method for controlling a vehicle drive unit having at least two individual engines, in which a total actual torque is continuously compared with an allowed total torque. The total actual torque is calculated from individual actual torque values of the at least two individual engines, and the allowed total torque is calculated from allowed individual torque values of the at least two individual engines. An error response is initiated when the comparison yields the result that the total actual torque is higher than the allowed total torque.